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From: crowl@cs.rochester.edu (Lawrence Crowl)
Newsgroups: comp.lang.c
Subject: Re: 16x16 = 32
Message-ID: <3293@sol.ARPA>
Date: Fri, 16-Oct-87 11:04:59 EDT
Article-I.D.: sol.3293
Posted: Fri Oct 16 11:04:59 1987
Date-Received: Sat, 17-Oct-87 20:42:04 EDT
References: <143@kesmai.COM>
Reply-To: crowl@cs.rochester.edu (Lawrence Crowl)
Organization: U of Rochester, CS Dept, Rochester, NY
Lines: 17

In article <143@kesmai.COM> dca@kesmai.COM (David C. Albrecht) writes:
>The point was that [Mark Williams] claimed that eliminating the extend to long
>was INCORRECT and would cause their compiler to fail acceptance testing.  That
>is what I think is BOGUS.  ... I was trying to see if anyone knew of an
>acceptance test or a VALID reason why not sign extending over the high bits is
>an INVALID result.

Many random number generators and hash functions rely on the result of an out
of range multiplication returning a result within the range, modulo (sort of)
the word size.  They rely on 7 + 3 == -6 for 4-bit two's complement words.

C does not provide integers, it provides words.  Words happen to have some
operations that are very similar to the operations we use for integers.
-- 
  Lawrence Crowl		716-275-9499	University of Rochester
		      crowl@cs.rochester.edu	Computer Science Department
...!{allegra,decvax,rutgers}!rochester!crowl	Rochester, New York,  14627